Old Europa News Stories & Citations

DOES MOON OF JUPITER HARBOR LIFE?

Discoveries made by the Voyager 2 spacecraft indicate life could
exist in a subsurface ocean on Europa, an ice-encased moon of the planet
Jupiter, a space agency consultant reports.

Richard C. Hoagland says he is convinced that the Voyager
data, gathered during fly-bys of Jupiter and its four moons last July,
establishes Europa as the most likely place in the solar system to search
for some form of life.

"Only three other objects in the solar system ever have been
seriously suggested as abodes of life - Mars, Jupiter and Saturn's moon
Titan," he said. "Spacecraft investigations of all three of these bodies
in recent years have cast doubt on life existing on any of them.

"Europa seems to have what these other worlds do not
- an ocean of water, the prime prerequisite for life as we know it,"
he said.

"The Voyager 2 findings leave little doubt that Europa
is covered with a crust of ice perhaps five miles thick that envelops
a global ocean possibly 60 miles deep," he wrote.

Hoagland suggests that at one time conditions were suitable
for this ocean to be free of ice.

"Jupiter was once a miniature sun according to our current
concepts of solar system formation," he said. "It only lasted a short
time - a few million years at most -but this was long enough, Hoagland
estimates, "for molecules that are suspected life-process precursors
to be created as they have been in thousands of earthly laboratory simulations.
As Jupiter's early star-like period ended, the ocean's surface soon
froze, locking the primordial soup' into an underground sea.

By Robert C. Cowen, Natural science editor of The Christian Science Monitor

Europa, the second of Jupiter's four large inner moons, appears to be able to
support organic life.

In reporting this, Ray Reynolds and Steven Squyres of the NASA
Ames Research Center emphasize that they make no claim that such life
actually exists.

However, by a combination of theoretical calculation and
data from ground-based studies and the Voyager spacecraft, they claim
to show that Europa probably is covered by an ocean of liquid water beneath
a relatively thin shell of ice. They note that this ice shell should be
thin enough in some places for sunlight to penetrate and support simple
organisms such as the microscopic ocean plants that live beneath Antarctic
ice on Earth.

''This in itself is interesting,'' Dr. -Reynolds says.
He adds, ''We think it's intriguing that conditions that can support life
should exist so far out in the solar system.''

Reynolds further explains that the main purpose of this
research is not to speculate about extraterrestrial life, but to ''lay
a framework for understanding'' satellites of the outer planets.

Europa has been especially challenging. Before the Voyager
1 and 2 flyby missions in March and July 1979, many scientists had expected
it to resemble Earth's moon. It turned out to be quite different.

Europa has a diameter of 3,130 kilometers (1,945 miles)
- about 15 percent smaller than our moon. Its density, three times that
of water, suggests a basically rocky body. But it could also have a lot
of water. Seen telescopically from Earth, it appears white, like a giant
snowball. So scientists were prepared to find an ice-covered body. But
they were surprised when Voyager photos showed it to have a smooth, billiard-ball
surface instead of a heavily cratered face like that of our moon.

In fact, only three craters have been identified in photos
of Europa. This indicates an active surface with something obliterating
craters rapidly after they are formed by incoming meteorites. Scientists
have been further puzzled by long dark streaks on the satellite's smooth
surface.

The model for Europa that Reynolds and Squyres have worked
out would, among other things, explain the absence of craters.

This model envisions an ocean 50 km. (31 mi.) deep with
an ice crust perhaps 5 km. (3 mi.) thick on average. The ocean would receive
heat energy from radioactive decay within the satellite, perhaps from
some volcanic action (although there is as yet no evidence for this),
and by the action of tidal forces of Jupiter. Heat flowing outward would
keep the ice at a subsurface temperature around 133 degrees below zero
C (-271 degrees F). This would be warm enough for the ice to be supple
and able to deform to smooth out craters, Reynolds says.

The two National Aeronautics and Space Administration (NASA)
scientists say another process also affects the surface. According to
their theory, Jupiter's tide-raising forces crack open the ice shell in
various places. Water boils up through the cracks into the vacuum of space
only to freeze and fall back onto the surface as frost. This would account
for the coating of what appears to a fluffy substance on top of the ice.

This fluffy coating evidently builds up rapidly, Reynolds
says. Jupiter's innermost large moon, Io, which has very active sulfur
volcanoes, leaves a sulfur trail in space. Some of this sulfur falls onto
Europa. But there is very little of it to be seen. To judge from the rate
at which it should accumulate, this implies that the frost is covering
up the surface very quickly, Reynolds says. The surface cracking is also
the key to the possibility of life-supporting conditions. Reynolds and
Squyres suggest that, when the cracks freeze over, the new ice should
be thin enough to let in sufficient sunlight to support some forms of
aquatic life.

The puzzling dark streaks may be regions where some of
the cracks open up, and they are large cracks themselves. Some scientists
have wondered if the darkening may be due to some kinds of organic chemicals
that form in these regions. Reynolds notes that, were there life in regions
where cracks form, there might be some organic products coming onto the
surface with the frost. But he emphasizes that this is pure speculation.

Within five to seven years' time, new ice formed over cracks
would become too thick to act as a window for photosynthesis. Nevertheless,
the two scientists conclude that enough new cracks would be constantly
opening to maintain something like 25 to 50 square km. (10 to 20 square
mi.) of livable habitat around the satellite.